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Specifications are subject to change without notice.
1
RevA0215
CT
T57
Programmable Capacitive Tuning IC
SON8
DESCRIPTION
The CTST570 is a digitally programmed capacitor specifically designed to tune a crystal or SAW based
oscillator to a desired center frequency. The desired capacitance value for production trimming is set by a
serial data stream when placed into a programming mode. The CTST570 is designed to be a labor and
cost saving device within the oscillator production process.
Using EEPROM technology, the capacitance can be re-tuned as needed during the production process by
repeating the programming steps thereby increasing production yield.
The CTST570 is available in an SON8 package (1.5mm x 1.0mm) for very small form factor oscillators.
ENGINEERING NOTES
Capacitor Structure
The CTST570 capacitance value is composed of three parallel capacitor banks, C
F
is a fixed capacitor
value of 2.6pF and C
MID
& C
LO
are variable capacitors of differing ranges and resolutions as seen in Table
1. Capacitors composing C
MID
and C
LO
are set with a binary control word through an 11-bit shift register
described in “Programming the CTST570” section. The values of each C
LO
and C
MID
stepping are detailed
in the complete Nominal Capacitance Binary Mapping spreadsheet.
C
TOTAL
=
C
F
+ C
MID
+ C
LO
Table 1 – Capacitor Structure
Internal
Capacitor
Min Value
(pF)
Max Value
(pF)
Step Size
(pF)
C
F
2.6 2.6 n/a
C
MID
0 9.8 1.4
C
LO
0 1.953 0.063
Total 2.6 14.353
BLOCK DIAGRAM
FEATURES
Capacitive Tuning Range of 2.6pF
to 14.55pF
0.063pF Minimum Step Size
Reprogrammable Through Non-
volatile EEPROM Storage
May Be Placed in Parallel for
Greater Capacitance Values
Very Low Supply Current
2.5V to 5.0V Supply Voltage
RoHS compliant Pb Free
Packages
